I agree that not all HD movies will knock you out of your seat or look noticably better than SD. However, if you watch BD for a while and then go back to SD the difference is quite dramatic. So stating that you have seen in store demos is not proof you are a good source of information regarding this topic. BTW store demos are rarely calibrated so your not even getting close to a good picture.
An observation I have made is that BD / HD DVD look better on the new fixed pixel digital displays (Plasma, LCD, DLP, LCoS) using an HDMI connection. CRT HDTVs do not give you the same pixel for pixel quality you get from these newer TVs. Spend a few hours on a 1080p LCD or DLP watching BD / HD DVD and I am sure all those sitting on the fence would have an easier time jumping in.